The pattern of pulsatile growth hormone secretion correlates with linear growth in animals. In order to provide insight into the role of endogenous growth hormone secretion in the regulation of altered growth velocity in both normal and pathophysiologic states, growth hormone levels will be determined at 20 minute intervals for 12 hours overnight. The effect of intrauterine events will be studied by comparing infants with intrauterine growth retardation with normal or reduced postnatal growth.